The invention relates to electrical circuit interrupters for capacitors, in particular, for dry capacitors of the metallized film type.
In a typical capacitor, a capacitor roll section is assembled in a container having a cover sealed thereto. Electrical connecting leads pass from the capacitor roll section in the container through the cover. In such a capacitor, failures result from internal arcing and thermal runaway, which cause gases to be formed in the capacitor roll section. These gases escape from the capacitor roll section and cause a pressure buildup in the container causing, in turn, the container, or the cover, to bulge to such an extent that the seal, or the container itself, fails. If such a capacitor is filled with a dielectric fluid, the fluid can then leak from the container causing damage to surrounding components and, if the fluid is flammable, a potential fire hazard.
In U.S. Pat. Nos. 3,377,510 to Rayno and 4,106,068 to Flannagan, there is disclosed a pressure-sensitive circuit interrupter combined with a fluid-filled electrical capacitor. The pressure buildup within the capacitor roll section is transmitted through the fluid to a deformable cover carrying connecting terminals. The deformation of this cover due to the transmitted pressure moves at least one of the terminals to such an extent that the electrical connection between this terminal and the capacitor roll section is broken. This removes the electrical potential on the capacitor roll section, which then ceases to produce gases therein thereby terminating the pressure buildup. The interrupter is dimensioned such that the electrical connection is broken by the deformation before the seal between the cover and the container, or the container itself, fails.
It has been suggested that this same type interrupter be used with dry metallized film capacitors. This has proven to be impractical since the air captured within the sealed container, unlike fluids, is compressible and does not as readily transmit the pressure buildup in the capacitor roll section. This leads to an inordinately long delay between the failure of the capacitor roll section and the breaking of the electrical connection, and the resulting generation of an increasing pressure differential between the interior of the capacitor roll section and the surrounding air in the container. This pressure differential may then be sufficient to rupture the container even though the electrical connection to the capacitor roll section is broken.